Typical connect/disconnect driveline systems for vehicles push torque through a torque coupling to the secondary axle to provide enhancements in performance, handling and mobility. These systems require that the secondary axle, and the rest of the driveline, be continually rotating, which reduces the overall efficiency of the vehicle, and reduces fuel economy.
Secondary axle disconnects are available and they permit the secondary axle and prop shaft to stop rotating. These disconnect systems increase vehicle efficiency, but they can be slow to react. The systems typically use an electric motor, gear reduction and a ball screw to compress a spring that will slide a collar to engage/disengage a shaft. Reaction times on the order of two seconds are common with these systems, which is too long to be effective during most handling events.
The current systems also require power to both engage and disengage a shaft and/or remain engaged or disengaged. The latter situation may require constant power to the system, which reduces overall system efficiency. Of course, if power is lost, the system remains in its last mode. In some applications, this is acceptable, but in other applications this is not preferred.
It would be desirable for a system to maintain vehicle efficiency, and to decrease reaction time to a level appropriate to deal with vehicle handling events. It would also be desirable for a system to automatically revert to a desired mode of operation in the event of a power failure.